The present invention is directed to a series of novel phthalocyanines suitable for use as photosensitizers for photodynamic therapy. More particularly, the present invention is directed to a series of new aluminum (Al) and silicon (Si) phthalocyanines having substituted amine or quaternary ammonium axial ligands, and the use of these new phthalocyanine compositions for the therapeutic treatment of cancer. In addition, the present invention is directed to the methods of synthesizing these new compositions.
Photodynamic therapy, hereinafter also referred to as "PDT", is a relatively new process for treating cancer wherein visible light is used to activate a substance, such as a dye or drug, which then attacks, through one or more photochemical reactions, the tumor tissue thereby producing a cell killing, or cytotoxic, effect. It has been discovered that when certain non-toxic photodynamic sensitizers, such as hematoporphyrin derivative ("HpD" or "Photofrin.RTM. I"), which is extracted from serum and/or components thereof, are applied intravenously, topically, intradermally, etc., to the human or animal body, they are selectively retained by the cancerous tissue while being eliminated by the healthy tissue. As a result, after the administration of a photodynamic substance and the waiting of a certain period of time depending upon the type of photosensitizer utilized (i.e. two to three days after HpD treatment), substantially higher levels of the photosensitizer are retained in the cancerous tissue.
The tumor or cancerous tissue containing the photosensitizer can then be exposed to therapeutic light of an appropriate wavelength and at a specific intensity for activation. The light can be directly applied through the skin to the cancerous area from a conventional light source (e.g. laser, sun lamp, white light sources with appropriate filters, etc.), or in cases where the cancerous tissue is located deeper within the body, through surgical or non-surgical entry such as by the use of fiber optic illumination systems, including flexible fiber optic catheters, endoscopic devices, etc. The light energy and the photosensitizer cause a photochemical reaction which kills the cell in which the photosensitizer resides.
As a result, by applying a photosensitizer to the animal or human body, waiting for a sufficient period of time for the photosensitizer to permeate throughout the body while dissipating from normal tissue more rapidly than from cancer tissue, and exposing the cancerous region during the sensitive period to suitable light of sufficient intensity, the preferential destruction of the cancerous tissue will occur.
The mechanisms by which the photosensitizers produce their killing effect on the host cells upon illumination by an appropriate light source are not precisely defined and are the subject of continuing research. However, it is thought that there are at least two general mechanisms by which the photosensitizers are chemically altered upon illumination. The first general reaction mechanism involves energy transfer from the excited photosensitizer to oxygen present in the cancerous tissue. The excited photosensitizer transfers its additional energy to the oxygen, producing singlet molecular oxygen (SMO or .sup.1 O.sub.2) which consequentially alters essential cell components.
More particularly, in the first general reaction mechanism, it is thought that the light energy causes the photosensitizer to become excited from the ground state, S.sub.0, to the first excited singlet state, S.sub.1. The photosensitizer's excited singlet state, S.sub.1, is then transformed by intramolecular coupling to the lowest lying triplet state T.sub.1. Through a direct intermolecular process discussed more particularly by John G. Parker of The John Hopkins University, Baltimore, Md., in U.S. Pat. Nos. 4,576,173; 4,592,361; and 4,827,938, the photosensitizer transfers this energy to oxygen molecules present in the tissue and raises them from the ground triplet to the first excited electronic singlet state .sup.1 O.sub.2. The singlet molecular oxygen, .sup.1 O.sub.2, destroys or alters vital cellular components such as the cell membrane, etc., ultimately inducing necrosis and destroying the cancerous tissue.
The process by which biological damage occurs as a result of the optical excitation of a photosensitizer in the presence of oxygen is generally referred to as "photodynamic action". A more detailed discussion concerning the use of photodynamic action in the treatment of cancer is discussed by Thomas J. Dougherty, William R. Potter, and Kenneth R. Weishaupt of Health Research, Inc., Buffalo, N.Y., in a series of patents, i.e. U.S. Pat. Nos. 4,649,151; 4,866,168; 4,889,129; and 4,932,934, concerning improved hematoporphyrin and porphyrin derivatives including dihematoporphyrin ether (DHE), the purified form of HpD, and methods utilizing same, for photodynamic therapy.
The second general mechanism thought to be involved in the killing effect produced by certain photosensitizers involves the production of free radicals. Subsequent reactions of the radicals with organic molecules and/or with oxygen results in the biochemical destruction of the diseased tissue.
Although the exact effective mechanisms of the photochemical reactions which produce death of the cancer cells is not clearly understood and varies depending upon the type of photosensitizer utilized, what is clear is that photodynamic therapy is effective for the preferential destruction of cancerous tissue. Furthermore, photodynamic therapy has several attractive features over conventional methods for treating cancer such as chemotherapy, radiation, surgical procedures, etc., in that the photosensitizers utilized are generally non-toxic, concentrate or remain preferentially in cancer cells, can be utilized with other modes of treatment since PDT does not interfere with other chemicals or processes, etc.
As a result, photodynamic therapy is now used experimentally for the treatment of malignant diseases in humans and animals. For example, photodynamic therapy has been used successfully for the treatment of a broad range of cancers including metastatic breast tumors, endometrial carcinomas, bladder tumors, malignant melanoma, Kaposi's sarcoma, basal cell carcinoma, chondrosarcoma, squamous cell carcinoma, prostate carcinoma, laryngeal papillomas, mycosis fungoides, superficial cancer of the tracheobronchial tree, cutaneous/mucosal papilloma, gastric cancer, enteric cancer, etc.
The drug in current clinical use is "Photofrin.RTM. II" a purified version of hematoporphyrin derivative (HpD, or "Photofrin.RTM. I"). HpD and Photofrin.RTM. II are complex mixtures of substances and have been the subject of numerous investigations to identify their active compounds. In addition, other porphyrins and porphyrin-like compounds such as chlorins (see U.S. Pat. Nos. 4,656,186; 4,693,885; and 4,861,876) and enlarged porphyrins, naphthalocyanines, phthalocyanines, platyrins, porphycenes (see U.S. Pat. Nos. 4,649,151 and 4,913,907), purpurins, texaphyrins, and verdins have been investigated as photosensitizers. Numerous other substances, such as "merocyanine 540", xanthenes (Rhodamine 123 6 G&B) cationic cyanic dyes, chalcogenapyryllium dyes, phenothiazinium derivatives, tetracycline, berbine sulphate, acridine orange, and fluorescein have also been used as photosensitizers, however, the porphyrin derivatives are generally preferred because they absorb in the long wave length region (red region) of the visible spectrum.
The specific reactions used by many of the above substances to produce the killing effect in cancer cells on exposure to excitatory light are in most instances not known or well understood. As mentioned above, research continues in this area in order to more fully understand the cytotoxic effects produced by the various photosensitizers.
Notwithstanding the above, although many of the above identified substances have demonstrated enhanced effects in photodynamic therapy, these substances also produce various side effects which limit their use for photodynamic therapy. The most predominant side effect exhibited by many of the currently utilized substances is the development of uncontrolled photosensitivity reactions in patients after the systemic administration of the photosensitizer and the exposure of the patient to normal sunlight. In this regard, on exposure to the sun, the photodynamic therapy patients can develop generalized skin photosensitization. As a result, the patient after receiving systemic injections of a photosensitizing substance is required to avoid bright light, especially sunlight for periods of about four to eight weeks.
Furthermore, since many of the above photosensitizers bind to other non-cancerous cells, some healthy cell destruction can also occur. Similarly, although many of the photosensitizers are soluble in water, large dosages are required for cellular uptake and/or treatment. Thus, use of many of the above indicated photosensitizers is normally limited to patients with severe cancerous tumors and continuing research is being conducted in order to produce photosensitizing substances, and/or methods of administering such substances, that avoid these side reactions as well as produce enhanced photosensitizing effects.
Considerable attention has recently been directed to a group of compounds having the phthalocyanine ring system. These compounds, called phthalocyanines, hereinafter also abbreviated as "Pc", are a group of photoactive dyes that are somewhat structurally similar (i.e. have nitrogen containing ring structure) to the porphyrin family. Phthalocyanines are azaporphyrins consisting of four benzoindole nuclei connected by nitrogen bridges in a 16-membered ring of alternating carbon and nitrogen atoms around a central metal atom (i.e. C.sub.32 H.sub.16 N.sub.8 M) which form stable chelates with metal cations. In these compounds, the ring center is occupied by a metal ion (such as a diamagnetic or a paramagnetic ion) that may, depending on the ion, carry one or two simple ligands. In addition, the ring periphery may be either unsubstituted or substituted.
Since E. Ben-Hur and I. Rosenthal disclosed the potential use of phthalocyanines as photosensitizers in 1985 (E. Ben-Hur and I. Rosenthal, The phthalocyanines: A new class of mammalian cell photosensitizers with a potential for cancer phototherapy, Int. J. Radiat. Biol. 47, 145-147, 1985), a great deal of research has followed producing a number of phthalocyanines for photodynamic therapy. Although prior studies with phthalocyanines have been generally disappointing, primarily because of the poor solubility characteristics of the basic ring, some of these compounds have attractive characteristics.
For example, unlike some of the porphyrin compounds, phthalocyanines strongly absorb clinically useful red light with absorption peaks falling between about 600 and 810 nm (Abernathy, Chad D., Anderson, Robert E., Kooistra, Kimberly L., and Laws, Edward R., Activity of Phthalocyanine Photosensitizers against Human Glioblastoma in Vitro, Neurosurgery, Vol. 21, No. 4, pp. 468-473, 1987). Although porphyrins absorb light poorly in this wavelength region, as a result of the increased transparency of biological tissues at longer wavelengths, red light is normally used for photodynamic therapy. Thus, the greater absorption of red light by the phthalocyanines over porphyrins indicates deeper potential penetration with the phthalocyanines in photodynamic treatment processes.
Furthermore, it has been found that the addition of certain metal cations (i.e. diamagnetic metal cations such as aluminum) to the phthalocyanine ring will, in some instances, create a fairly stable chelate with enhanced photosensitizing tumoricidal activity. While the mechanisms for producing the photoreactions are not clear (i.e. it is not known whether singlet oxygen or hydroxyl radicals, etc. are produced), the choice of the metal cation is apparently critical in that certain metals (i.e., paramagnetic metals) may actually inhibit the phototoxic properties of the resulting compound. Abernathy, et al., pp. 470-471.
In addition, the phthalocyanines offer many benefits over the porphyrin components as photosensitizers in that the phthalocyanines are relatively easy to synthesize, purify, and characterize in contrast to the porphyrins, which are often difficult to prepare. Similarly, the metal phthalocyanines are exceptionally stable compounds in comparison to the porphyrin or porphyrin-like compounds. As a result, certain metallic phthalocyanines, such as aluminum phthalocyanine tetrasulfonate (AlPcS) and chloroaluminum phthalocyanine (AlPcCl), offer a number of advantages over porphyrins as therapeutic agents for photodynamic therapy.
However, notwithstanding some of the benefits indicated above, only a few of the many possible types of ring-substituted phthalocyanines belonging to this group have been examined. By far the most attention has been given to sulfonated phthalocyanines and to phthalocyanines with peripheral substituents carrying hydroxy, alkoxy, and amino substituents. Very little attention has been given to phthalocyanines with complex metal ligands.
The limited variety of phthalocyanines which have been tested vary greatly i their photosensitizing activity Metal-free phthalocyanines show poor photodynamic activity (Abernathy, C. D., R. E. Anderson, K. L. Kooistra, & E. R. Laws, Jr., "Activity of Phthalocyanine Photosensitizers Against Human Glioblastoma in vitro", Neurosurgery 21, pp 468-473, 1987; Chan, W. S., J. F. Marshall, G. Y. F. Lam, & I. R. Hart, "Tissue Uptake, Distribution, and Potency of the Photoactivatable Dye Chloroaluminum Sulfonated Phthalocyanine in Mice Bearing Transplantable Tumors", Cancer Res.) 48, pp 3040-3044, 1988, Sonoda, M., C. M. Krishna, & P. Riesz, "The Role of Singlet Oxygen in the Photohemolysis of Red Blood Cells Sensitized by Phthalocyanine Sulfonates", Photochem Photobiol. 46, pp. 625-632, 1987) as do phthalocyanines containing paramagnetic metals. In contrast, those containing diamagnetic metals, such as Al, Sn, and Zn, are active as a result of the long half-life of the triplet state (Chan, W. S., J. F. Marshall, G. Y. F. Lam, & I. R. Hart, "Tissue Uptake, Distribution, and Potency of the Photoactivatable Dye Chloroaluminum Sulfonated Phthalocyanine in Mice Bearing Transplantable Tumors", Cancer Res. 48, pp. 3040-3044, 1988; Sonoda, M., C. M. Krishna, & P. Riesz, "The Role of Singlet Oxygen in the Photohemolysis of Red Blood Cells Sensitized by Phthalocyanine Sulfonates", Photochem. Photobiol. 46, pp. 625-632, 1987). While in general there appears to be an increase in photosensitizing ability with lipophilicity (Berg, K., J. C. Bommer, & J. Moan, "Evaluation of Sulfonated Aluminum Phthalocyanines for use in Photochemotherapy. Cellular Uptake Studies", Cancer Letters 44 pp. 7-15, 1989) some highly lipophilic derivatives, such as a tetraneopentoxy derivative, are poor photosensitizers (Rosenthal, I., E. Ben-Hur, S. Greenberg, A. Concepcion-Lam, D. M. Drew, & C. C. Leznoff, "The Effect of Substituents on Phthalocyanine Phototoxicity", Photochem. Photobiol. 46, pp. 959-963, 1987).
Recently, Leznoff, et al. (Leznoff, C. C., Vigh, S., Svirskaya, P. I., Greenberg, S., Drew, D. M., Ben-Hur, E. & Rosenthal, I., "Synthesis and Photocytoxicity of Some New Substituted Phthalocyanines", Photochem. Photobiol. 49, pp. 279-284, 1989) synthesized a series of ring-substituted phthalocyanines. The substituents were hydroxy or alkoxy groups, as well as substituted amines. Of this series, a Zn phthalocyanine with four diethylaminopropyl groups was reported to have some photosensitizing activity against Chinese hamster fibroblast V79 cells in culture. However, it is critical to note that although amine groups were present in the Zn phthalocyanine compound containing the four diethylaminopropyl groups, the amine groups were ring substituents and no simple axial ligands were specified. For some time the applicants have been searching for phthalocyanines having superior photosensitizing ability. In this search, the applicants have emphasized compounds with complex metal ligands. Initially, applicants examined the photocytotoxicity of twenty-one phthalocyanines taken from a collection in the applicants' laboratories to Chinese hamster fibroblasts, i.e. V79 cells. One of these phthalocyanines was HOSiPcOSi(CH.sub.3).sub.2 (CH.sub.2).sub.3 OCH.sub.2 --CHOHCH.sub.2 N(C.sub.2 H.sub.5).sub. 2, a phthalocyanine composition carrying a hydroxyl amine functional group. This was found to be taken up efficiently by the Chinese hamster fibroblast V79 cells and to have excellent photocytotoxicity. However, solutions of this composition in dimethylformamide were found to decompose relatively rapidly. Further, it appeared that the composition might have dark toxicity (i.e. be toxic to tissues in the absence of light) in vivo because of its --OCHOHCH.sub.2 NR.sub.2 functional group.
With the results of this preliminary work in mind, the applicants then prepared and studied a series of new aluminum and silicon phthalocyanines having relatively simple ligands carrying NR.sub.2 or NR.sub.3 + functions. The present invention is the result of applicants' studies of these compounds, and the use of the same for photodynamic therapy.